Electrochemical process for the production of synthesis gas using atmospheric air and water

ABSTRACT

A process is provided for synthesizing synthesis gas from carbon dioxide obtained from atmospheric air or other available carbon dioxide source and water using a sodium-conducting electrochemical cell. Synthesis gas is also produced by the coelectrolysis of carbon dioxide and steam in a solid oxide fuel cell or solid oxide electrolytic cell. The synthesis gas produced may then be further processed and eventually converted into a liquid fuel suitable for transportation or other applications.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a divisional application of, and claims priority to, U.S.application Ser. No. 11/467,524 filed Aug. 25, 2006 now U.S. Pat. No.8,075,746, which claimed priority to U.S. Provisional Application No.60/711,252 filed Aug. 25, 2005. Both of these applications areincorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates in general to methods for producingsynthesis gas from easily obtainable precursors, and more particularly,to the generation of such synthesis gas from atmospheric air and water.

BACKGROUND OF THE INVENTION

Users of fuels such as gasoline and diesel (in commercial applications)and JP-8, F-76 and other similar fuels (in military applications) havebenefited from the existence of an extensive and well-establishedinfrastructure for their shipping, delivery to end users, and use. Thepresence of this infrastructure has also enabled technology developmentof liquid fuel-based systems for uses ranging from automobiles tomilitary aircraft. Within areas well-served by this infrastructure,dependence upon such liquid fuel-based systems is largely unquestioned.

In some applications, however, continued dependence on the availabilityof such liquid fuel products is unwise. Such applications includeindustrial or commercial applications in primitive regions and militaryoperations in remote locations away from standard supply systems andsources. In applications such as military logistics supporting extendednaval missions, assuring the availability of a steady and sufficientsupply of liquid fuel products may become critically important and verydifficult. While all-electric-powered ships and aircraft are planned,moves toward these platforms are slow and their completion is still onlyforeseen in the somewhat distant future. It is anticipated that atransition away from liquid fuels will be simpler and more rapidlyadopted in larger apparatus such as aircraft carriers via the use ofon-board nuclear power plants than in smaller equipment such asaircraft.

As a result, it is anticipated that reliance upon liquid fuel-basedsystems will continue well into the foreseeable future. It would thus bebeneficial to provide new methods and systems for generating liquidfuels using electricity and commonly-available resources that could beemployed on-location to reduce the criticality of long supply chains.The availability of such a process based on plentiful electricity andcommon resources could speed conversion to all-electric power sources insome simpler applications while retaining support for others in whichelectric power-based systems are either difficult or impractical.

Such methods and systems are provided herein.

BRIEF SUMMARY OF THE INVENTION

The present invention is directed to processes, methods, and systems forthe production of synthesis gas for fuel production or otherapplications. The processes, methods, and systems of the presentinvention utilize commonly-available resources as inputs and rely uponelectricity to provide synthesis gas as an output.

The present invention includes an electrochemical cell for producingsynthesis gas. In one embodiment within the scope of the invention, theelectrochemical cell includes an anode chamber containing anelectrochemically active anode. Water is decomposed at the anode toproduce oxygen and hydrogen ions. The oxygen is preferably collected andremoved from the anode chamber. A source of sodium carbonate is providedwhich reacts with the hydrogen ions and decomposes to form carbondioxide, water, and sodium ions. The carbon dioxide is preferablycollected and removed.

In one embodiment, the anode chamber is divided by a separator,permeable to hydrogen ions, to form an intermediate chamber. Theseparator which permits transport of hydrogen ions may be a microporousseparator, a cation exchange membrane, a mesh or a screen. In thisembodiment, the sodium carbonate is added to the intermediate chamber.The anode chamber need not be divided by a separator, but a separatormay facilitate collection and removal of the oxygen and carbon dioxidegases. It may also eliminate the need for later separation of carbondioxide from oxygen.

The electrochemical cell includes a cathode chamber containing anelectrochemically active cathode separated from the anode chamber, orintermediate chamber, by a membrane which permits transport of Na⁺ ions.The membrane which permits transport of Na⁺ ions is preferably a sodiumsuper ionic conductor ceramic material, a cation exchange membrane, orother similar membrane.

Water is reduced in the cathode chamber to produce hydrogen gas andhydroxyl ions. The hydroxyl ions combine with sodium ions to form sodiumhydroxide. The hydrogen gas is collected and removed from the cathodechamber.

The system or process includes means for facilitating the reaction ofCO₂ and H₂ to form synthesis gas comprising CO and additional H₂. Suchmeans may include a catalyst exposed to the mixture of CO₂ and H₂. Thecatalyst may be a watergas shift catalyst or a Fischer-Tropsch catalyst.The mixture of CO₂ and H₂ may alternatively be heated to enable ahomogenous gas phase equilibrium reaction with CO and H₂O. The means forfacilitating the reaction of CO₂ and H₂ to form synthesis gas mayinclude an oxygen ion conducting electrolysis cell to cause electrolysisof CO₂ to CO, which with the H₂ comprises synthesis gas.

In the foregoing embodiment, sodium hydroxide is preferably removed fromthe cathode and reacted with a source of carbon dioxide to form sodiumcarbonate which may replenish the sodium carbonate decomposed in theanode chamber. The source of carbon dioxide includes, but is not limitedto atmospheric air, combustion gases, and aerobic decomposition gases.

The electrochemical cell may be embodied within a plurality of stackedelectrochemical cells separated by bipolar plates. The use of stackedelectrochemical cells may enable the efficient production of largequantities of synthesis gas.

The electrochemical cell may perform a process for producing synthesisgas by decomposing water within an anode chamber according to thefollowing reaction: ½H₂O→¼O₂ +H⁺+e⁻ and removing oxygen from the anodechamber. Na₂CO₃ and H⁺ ions may react within anode chamber according tothe following reaction: H⁺+½Na₂CO₃→½CO₂+½H₂O+Na⁺. This reactionpreferably occurs at a location a distance away from the anode butwithin the anode chamber. The process includes the steps of removing CO₂from the anode chamber at a location near where it is produced andtransporting Na⁺ ions from the anode chamber to a cathode chamber. Waterdecomposes within the cathode chamber according to the followingreaction: Na⁺+H₂O+e⁻→NaOH+½H₂. H₂ is collected and removed from thecathode chamber. The collected CO₂ and H₂ react to form synthesis gascomprising CO and H₂. NaOH may be removed from the cathode chamber,reacted with carbon dioxide to form Na₂CO₃, and transported to the anodeto replenish the Na₂CO₃ consumed in the reaction with hydrogen ions.

Another embodiment within the scope of the invention includes anelectrochemical device for the coelectrolysis of carbon dioxide andsteam to produce synthesis gas. This electrochemical device includes anoxygen ion conducting membrane, a cathode attached to one surface of theoxygen ion conducting membrane and an anode attached to an oppositesurface of the oxygen ion conducting membrane. The cathode iselectrochemically active for reduction of steam to form hydrogen andoxygen ions. The anode is electrochemically active for recombination ofoxygen ions into oxygen molecules.

A source of steam and carbon dioxide may contact the cathode underconditions which cause the following reactions to occur: H₂O+2e⁻→H₂+O⁻²,CO₂+2e⁻→CO+O⁻² and CO₂+H₂

CO+H₂O. Synthesis gas comprising CO and H₂ is collected and recovered atthe cathode, and oxygen ions are conducted through the oxygen ionconducting membrane to the anode where they are recombined to form O₂,which is collected and recovered.

The cathode preferably comprises a mixture of nickel oxide and anotheroxide. In one embodiment, the cathode comprises a first metal oxide anda solid solution of nickel oxide and a second metal oxide selected fromthe group consisting of magnesium oxide, cobalt oxide, copper oxide, andmixtures thereof. The second metal oxide is preferably present in anamount from 1 to 50 mole % relative to the nickel oxide. In oneembodiment, the first metal oxide is zirconia doped with one or moreoxides selected from the group consisting of yttrium oxide, ytterbiumoxide, calcium oxide, magnesium oxide, and scandium oxide. In anotherembodiment, the first metal oxide is ceria doped with one or more oxidesselected from samarium oxide, gadolinium oxide, yttrium oxide, ytterbiumoxide, calcium oxide, magnesium oxide, and scandium oxide. In yetanother embodiment, the first metal oxide is lanthanum gallium oxidedoped with one or more elements selected from strontium, magnesium,iron, and cobalt. The cathode preferably comprises a surface dispersedcatalyst selected from the group consisting of Pr, Co, Ce, Eu, otherrare earth elements and mixtures thereof.

The anode preferably comprises a mixture of perovskite and an oxide. Inone embodiment, the anode comprises a mixture of perovskite and an anodeoxide, wherein the perovskite is (Pr_(1-x)La_(x))_(z-y)A_(y)BO_(3-δ),where A is an alkaline earth metal selected from Sr and Ca and mixturesthereof, B is a transition metal selected from Mn, Co, Fe, and mixturesthereof, with 0≦x≦1, 0≦y≦0.5, 0.8≦z≦1.1, δ is an oxygennon-stoichiometry value, wherein the anode oxide is selected fromzirconia doped with one or more of yttrium oxide, ytterbium oxide,calcium oxide, magnesium oxide, scandium oxide, and cerium oxide andceria doped with one or more of yttrium oxide, ytterbium oxide, calciumoxide, magnesium oxide, scandium oxide, and zirconium oxide. Onepresently preferred perovskite material is Pr_(0.8)Sr_(0.2)MnO_(3-δ).The anode preferably comprises a surface dispersed catalyst selectedfrom the group consisting of Pr, Co, Ce, Eu, other rare earth elements,Sr, Ca, and mixtures thereof.

The source of carbon dioxide is preferably selected from atmosphericair, combustion gases, or aerobic decomposition gases.

Other advantages and aspects of the present invention will becomeapparent upon reading the following description of the drawings anddetailed description of the invention. These and other features andadvantages of the present invention will become more fully apparent fromthe following figures, description, and appended claims, or may belearned by the practice of the invention as set forth hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

In order that the manner in which the above-recited and other featuresand advantages of the invention are obtained will be readily understood,a more particular description of the invention briefly described abovewill be rendered by reference to specific embodiments thereof that areillustrated in the appended drawings. Understanding that these drawingsdepict only typical embodiments of the invention and are not thereforeto be considered to be limiting of its scope, the invention will bedescribed and explained with additional specificity and detail throughthe use of the accompanying drawings in which:

FIG. 1 is a schematic view of a two-compartment electrochemical cell forgenerating synthesis gas within the scope of the present invention;

FIG. 2 is a schematic view of an electrochemical cell for generatingsynthesis gas showing recycle of NaOH and regeneration of NaCO₃ andcapture and separation of CO₂;

FIG. 3 is a schematic view of an oxygen ion conducting electrolysis celluseful in generating synthesis gas;

FIG. 4 is a schematic view of a three-compartment electrochemical cellfor generating synthesis gas within the scope of the present invention;

FIG. 5 is a schematic view of a synthesis gas generating system whichproduces synthesis gas from the coelectrolysis of steam and carbondioxide; and

FIG. 6 is a schematic view of another oxygen ion conducting electrolysiscell useful in generating synthesis gas.

DETAILED DESCRIPTION OF THE INVENTION

The presently preferred embodiments of the present invention will bebest understood by reference to the drawings, wherein like parts aredesignated by like numerals throughout. It will be readily understoodthat the components of the present invention, as generally described andillustrated in the figures herein, could be arranged and designed in awide variety of different configurations. Thus, the following moredetailed description of the embodiments of the processes, methods, andsystems for the production of synthesis gas for fuel or otherapplications of the present invention, as represented in FIGS. 1 through6, is not intended to limit the scope of the invention, as claimed, butis merely representative of presently preferred embodiments of theinvention.

In a first embodiment of the processes of the present invention, aprocess is disclosed for producing synthesis gas, also known as“syngas,” comprising a mixture of CO and H₂. This process 10 isillustrated schematically in FIG. 1. The process 10 utilizes atwo-compartment electrochemical cell 12. The electrochemical cellincludes an anode compartment or chamber 14 and a cathode compartment orchamber 16. A sodium-conducting membrane 18 separates the anode chamber14 from the cathode chamber 16. Suitable sodium-conducting membranes 18include NaSICON (sodium (Na) Super Ionic CONductor) ceramic materials,as well as other ceramic and polymer cation exchange membranes known topersons skilled in the art.

The anode chamber 14 includes an electrochemically active anode 20 and asource of water in which the water (H₂O) is decomposed according to thefollowing reaction:½H₂O→¼O₂+H⁺+e⁻  (1)The O₂ is collected and removed from the anode chamber 14.

In this process 10, sodium carbonate (Na₂CO₃) is decomposed in the anodechamber 20 of the electrochemical cell 12 to produce carbon dioxide(CO₂) according to the following reaction:H⁺+½Na₂CO₃→½CO₂+½H₂O+Na⁺  (2)The CO₂ is collected and removed from the anode chamber 14. Sodium ionsare transferred across the sodium-conducting membrane 18. A source ofsodium carbonate is provided sufficiently close to the anode 14 so thatthe sodium carbonate reacts with H⁺ ions in solution. It may bepreferred to space the sodium carbonate a sufficient distance away fromthe anode to facilitate separate removal of the O₂ produced at the anode14 and the CO₂ produced by the decomposition of sodium carbonate. Sodiumcarbonate may be directly provided for use in the cell 12, or mayalternatively be readily obtained by the reaction of sodium hydroxidewith a carbon dioxide source according to the following reaction:NaOH+½CO₂→½Na₂CO₃+½H₂O  (3)Examples of typical carbon dioxide sources include, but are not limitedto, atmospheric air, combustion gases, or aerobic decomposition gases.Aerobic decomposition gases include gases naturally produced upondecomposition of various organic materials, including waste materials.

The cathode chamber 16 includes an electrochemically active cathode 22and a source of water in which the water is reduced according to thefollowing reaction:Na⁺+H₂ O+e ⁻→NaOH+½H₂  (4)The H₂ is collected and removed from the cathode chamber. The NaOH mayoptionally be collected and removed from the cathode chamber, as shownby NaOH stream 24 in FIG. 2. As mentioned above, sodium hydroxide may bereacted with a source of carbon dioxide 26 to form sodium carbonatewhich may be recycled to the anode chamber as a sodium carbonate source28, shown in FIG. 2.

By applying an electrical potential across the two-compartment cell 12,water and sodium carbonate are decomposed and produce a flow 30 ofoxygen and a flow 32 of carbon dioxide. The reduction of water at thecathode 22 generates hydroxyl ions and a flow 34 of hydrogen gas. As thesodium ions migrate through the membrane 18 from the anolyte side (anodechamber 14) of the cell 12 to the catholyte side (cathode chamber 16),they will combine with the hydroxyl ions produced by the reduction ofwater to form sodium hydroxide solution as shown in reaction (4).

During operation of the electrochemical cell 12, oxygen and carbondioxide may be collected as separate gas flows 30, 32 or they may bemixed gases 36, shown in FIG. 2. If mixed, the oxygen is preferablyseparated from the carbon dioxide in a carbon dioxide separator 38 sothat the carbon dioxide may be used in subsequent process steps. Carbondioxide separation in carbon dioxide separator 38 may be conducted usingvarious processes known to those of ordinary skill in the art. Suchprocesses include, but are not limited to, use of activated carbon ormolecular sieves to absorb CO₂ from the gases removed from the cathode14. Such techniques often utilize multiple absorption beds which arerotated such that those which are full are rotated out of the gas streamand stripped prior to continued use. Other methods include filtration ofthe gas stream 36 using a polymeric membrane selectively permeable byeither O₂ or CO₂, or using CO₂-absorbent fluids such as amine solutionspresented to the gas stream 36 as in a scrubber unit. Oxygen may beseparated from carbon dioxide by exposing the mixed CO₂ and O₂ gasstream to an oxygen-conducting membrane such as yttria-stabilizedzirconia (or “YSZ”) to extract the oxygen. Other methods of separatingCO₂ and O₂ are well known to those of ordinary skill in the art and maybe implemented within the scope of the invention.

The cathode chamber 16 of this embodiment of the electrochemical cell 12contains water and sodium hydroxide as the catholyte. In the cathodechamber 16, water is reduced in the presence of sodium ions to release aflow of hydrogen gas 34 and form sodium hydroxyide. Thus, the reactionsconducted in the electrochemical cell 12 may be represented as follows:

-   -   Anode H₂O→½O₂+2 H⁺+2e⁻        -   2H⁺+Na₂CO₃→CO₂+H₂O+2 Na⁺        -   Na₂CO₃ (aq)→CO₂+½O₂+2 Na⁺+2e⁻(overall)    -   Cathode 2Na⁺+2H₂O+2 e⁻→2NaOH+H₂    -   Overall Na₂CO₃+2H₂O→2NaOH+CO₂+H₂+½O₂

The CO₂ flow 32 from the anode chamber 14 and the H₂ flow 34 from thecathode chamber 16 may be combined and further processed to convert theCO₂ into CO to form syngas 40. CO₂ and H₂ may react to form thecomponents of the syngas mixture 40 (CO+H₂). Syngas may be obtained fromCO₂ and H₂ according to one or more of the following reactions:CO₂+2e ⁻→CO+O⁻²  (5)CO₂+H₂→CO+H₂O  (6)

It should be noted that such syngas mixtures 40 may also include amountsof CO₂ and H₂O. Means may be provided to facilitate the reaction of CO₂and H₂ to form synthesis gas. Such means may include a catalytic reactor42 in which a suitable catalyst is exposed to the mixture of CO₂ and H₂,as shown in FIG. 2 For example, the catalyst may be a watergas shiftcatalyst, also known as a shift catalyst or reverse shift catalyst. Thecatalyst may comprise a Fischer-Tropsch catalyst. The CO₂ and H₂ gasesmay be heated to facilitate a homogenous gas phase equilibrium reaction.Other means to facilitate the reaction of CO₂ and H₂ to form synthesisgas may comprise an oxygen ion conducting electrolysis cell 44 to causeelectrolysis of CO₂ and form CO and O₂. The CO is collected, and withH₂, forms synthesis gas.

A schematic representation of an oxygen ion conducting electrolysis cell44 is shown in FIG. 3. Cell 44 includes an oxygen ion conductingmembrane 46. A variety of materials may be used to fabricate the oxygenion conducting, including but not limited to, yttria-stabilized zirconia(“YSZ”). The electrochemical device for the electrolysis of carbondioxide to product carbon monoxide may also include a source of carbondioxide in contact with a cathode 48. The cathode 48 is attached to asurface of the oxygen ion conducting membrane 46 which iselectrochemically active to reduce carbon dioxide to form carbonmonoxide and oxygen ions according to reaction (5), above. CO iscollected and recovered at the cathode the oxygen ions are conductedthrough the oxygen ion conducting membrane to the and anode 50. Theanode 50 is attached to an opposite surface of the oxygen ion conductingmembrane 42 which is electrochemically active for recombination ofoxygen ions into oxygen molecules, according to the following reaction:O⁻²→½O₂+2e ⁻  (7)

The cathode 48 and anode 50 should be sufficiently permeable to allowdiffusion of carbon dioxide, oxygen, or other gaseous species that mayreact or be produced at the interface of the oxygen ion conductor 46 andthe cathode 48 and the interface of the oxygen ion conductor 46 and theanode 50. By applying an electrical potential across the oxygen ionconducting electrolysis cell 44, carbon dioxide is reduced to formcarbon monoxide and oxygen. It produces a flow 52 of carbon monoxide anda flow 54 of oxygen. The reduction of carbon dioxide at the cathode 48generates oxygen ions and the flow 52 of carbon monoxide. As the oxygenions migrate through the membrane 46 from the cathode 48 to the anode 50they will combine to form oxygen as shown in reaction (7), above.

The materials and configurations used for the cathode 48 and anode 50may be the same or similar to those used in connection with the cathodeand anode described below in connection with FIG. 6.

This syngas mixture 40 can be further processed to produce liquidhydrocarbon fuel using any suitable process available in the art. Onesuch process commonly used to convert syngas 40 to liquid fuel is theFischer-Tropsch process, in which syngas 40 is reacted in the presenceof a catalyst (such as an iron or cobalt catalyst) to produce liquidhydrocarbon fuels. Other suitable processes, including variations on theFischer-Tropsch process, are known to those of ordinary skill in theart, and could be used with the processes of the present invention. Herethe term liquid hydrocarbon fuel also includes lighter hydrocarbons suchas methane, ethane, propane, butane, etc. which may be vapors at ambientconditions but which also may be liquefied under pressure or cryogenticconditions. A typical Fischer-Tropsch process produces a widedistribution of hydrocarbon chain length, all having fuel value.

The processes and systems of the present invention further allow forreplenishment of the electrochemical cell 12 usinggenerally-readily-available materials. As mentioned above in relation toFIG. 2, the NaOH generated in the cathode chamber 16 may be recycled inNaOH stream 24 and reacted with CO₂ source 26, such as CO₂ inatmospheric air, via a spontaneous reaction (encouraged by heat) togenerate the sodium carbonate. The regenerated sodium carbonate or othersodium carbonate source 28 may replenish the sodium carbonate consumedin the anode chamber 14. Various systems for speeding this process areavailable and known to one of ordinary skill in the art. This allows theanode chamber 14 to be replenished. The cathode chamber 16, on the otherhand, may be replenished by adding water 56. Alternatively, the sodiumcarbonate regeneration step may be skipped and the electrochemical cellmay be replenished by direct supply of sodium carbonate. Thus, thisembodiment of the processes of the present invention only requireselectric power, CO₂ from a carbon source or from atmospheric air, andwater as the only inputs needed to generate syngas.

In another embodiment within the scope of the present invention, athree-compartment electrochemical cell 60 is provided. Cell 60, shown inFIG. 4, is similar to cell 12, except that the anode chamber 14 includesa separator 62 which allows transport of H⁺ ions. Suitable separatorsmay include a microporous separator, cation exchange membrane, a mesh ora screen. In this embodiment, the separator 62 defines an intermediatechamber 64 disposed between the separator 62 and the sodium-conductingmembrane 18. Water is decomposed at the anode 20 according to reaction(1), above. Sodium carbonate is decomposed in the intermediate chamberaccording to reaction (2), above. The three-compartment electrochemicalcell may facilitate collection, separation and removal of the productgases, oxygen, carbon dioxide, and hydrogen. A separate process forseparating carbon dioxide from oxygen may not be required. In addition,a plurality of three-compartment electrochemical cells 60, separated bybipolar plates, may be stacked or connected in a way to efficientlygenerate large quantities of carbon dioxide and hydrogen for use inproducing synthesis gas.

In yet another embodiment of the methods of the present invention,syngas 40 may be produced by the coelectrolysis of carbon dioxide andsteam. FIG. 5 includes a diagram of this process 100. In this process100, a flow 102 of carbon dioxide is provided from a carbon dioxidesource 104, such as discussed above. The carbon dioxide source mayinclude a gas separator, discussed above, to separate carbon dioxidefrom atmospheric air. The process 100 also includes a flow of steam 106provided from a source of steam 108. The carbon dioxide flow 102 andsteam flow 106 are sent to a solid oxide electrolysis cell (SOEC) 110.Electricity 120 and any required heat are provided to the cell 110 todrive the following reactions:CO₂+2e ⁻→CO+O²  (5)H₂O+2e ⁻→H₂+O⁻²  (8)O⁻²→½O₂+2e ⁻  (7)The following additional reaction may also occur in the SOEC 110:CO₂+H₂

CO+H₂O  (6)The net equation of the SOEC is shown as follows:H₂O+CO₂→H₂+CO+O₂  (9)

In the SOEC 110, oxygen is stripped from the incoming CO₂ 102 and H₂O106 (as steam) by an oxygen ion-conducting electrolysis cell 140,similar to the electrolysis cell 44, discussed above and illustrated inFIG. 3. FIG. 6 shows that electrolysis cell 140 includes an oxygen ionconducting membrane 142. A variety of materials may be used to fabricatethe oxygen ion conducting, including but not limited to,yttria-stabilized zirconia (“YSZ”). A cathode 144 is attached to asurface of the oxygen ion conducting membrane 142 which iselectrochemically active to reduce carbon dioxide to form carbonmonoxide and oxygen ions according to reaction (5), above, and alsoelectrochemically active to reduce steam (water) to form hydrogen gasand oxygen ions according to reaction (8), above. An anode 146 isattached to an opposite surface of the oxygen ion conducting membrane142 which is electrochemically active for recombination of oxygen ionsinto oxygen molecules, according to reaction (7), above.

The cathode 144 and anode 146 should be sufficiently permeable to allowdiffusion of carbon dioxide, steam, oxygen, or other gaseous speciesthat may react or be produced at the interface of the oxygen ionconductor 142 and the cathode 144 and the interface of the oxygen ionconductor 142 and the anode 146.

By applying an electrical potential across the oxygen ion conductingelectrolysis cell 140, carbon dioxide and water are reduced to formcarbon monoxide, hydrogen, and oxygen. It produces a flow 150 of carbonmonoxide, a flow 152 of hydrogen, and a flow 154 of oxygen. Thereduction of carbon dioxide and steam at the cathode 144 generatesoxygen ions and the flow 150 of carbon monoxide and flow 152 ofhydrogen. As the oxygen ions migrate through the membrane 142 from thecathode 144 to the anode 146 they will combine to form oxygen as shownin reaction (7), above.

This syngas mixture 40 can be further processed to produce liquidhydrocarbon fuel using any suitable process available in the art.

The carbon dioxide and steam are reduced at the cathode side 144 of theoxygen-ion conducting membrane. Oxygen ions are transported through theoxygen ion conducting membrane 142 and evolved at the anode 146 asoxygen gas. The SOEC 110 provides an outflow 122 of O₂. As with theprocess 10 of the invention, this process 100 results in an outflow 122of O₂ and a separate stream of syngas 124 comprising CO, and H₂. Theoxygen may be produced at high purity without any subsequent separationrequired. As also discussed above, the syngas 124 may be furtherprocessed to produce a liquid hydrocarbon fuel suitable for use withcurrent equipment using known methods.

The anode may be a mixture of perovskite and an oxide. In oneembodiment, the anode consists of a perovskite and an oxide mixed in thevolume ratio of oxide, 0≦V_(oxide)≦70%. The anode perovskite may be(Pr_(1-x)La_(x))_(z-y)A_(y)BO_(3-∂) where A is an alkaline earth inparticular Sr or Ca, and B is a transition metal in particular Mn, Coand Fe and mixtures thereof, with 0≦x≦1.0, 0≦y≦0.5, 0.8≦z≦1.1. ∂ is theoxygen non-stoichiometry determined by the crystalline chemistry andelectro-neutrality conditions. The anode oxide may be zirconia dopedwith one or more of yttrium oxide, ytterbium oxide, calcium oxide,magnesium oxide, scandium oxide, and cerium oxide. The anode oxide couldalso be ceria doped with one or more of yttrium oxide, ytterbium oxide,calcium oxide, and magnesium oxide, scandium oxide, and zirconium oxide.In one embodiment, the oxide doping in zirconia and ceria ranges fromabout 2 to about 15 mole %.

The cathode may be a mixture of nickel oxide and an oxide. In oneembodiment, the nickel oxide is a solid solution with magnesium oxide.The cathode solid solution may contain between about 1 to about 25 mole% magnesium oxide relative to the nickel oxide. The nickel oxide in thesolid solution is reduced to nickel during cell operation. The oxide inthe cathode may include one of the group of zirconia, ceria, andmixtures thereof. The zirconia in the cathode may be doped with one ormore of yttrium oxide, ytterbium oxide, calcium oxide, magnesium oxide,and scandium oxide. Ceria in the cathode may be doped with one or moreof samarium oxide, gadolinium oxide, yttrium oxide, ytterbium oxide,calcium oxide, magnesium oxide, and scandium oxide.

The anode and cathode may be infiltrated with a catalyst material. Thecatalyst may be a surface dispersed catalyst selected from one of thegroup of Pr, Co, Ce, Eu, other rare earth elements, and combinationsthereof. The catalyst in addition may contain one or more of Sr and Ca.The catalyst may be infiltrated as a salt soluble in water or an organicsolvent. The catalyst may also be infiltrated as oxide particles.

A source of steam and carbon dioxide in contact with the cathode 144under conditions which cause the following reactions to occur:H₂O+2e⁻→H₂+O⁻², CO₂+2e⁻→CO+O⁻² and CO₂+H₂→CO+H₂O, wherein synthesis gascomprising CO and H₂ is collected and recovered at the cathode andwherein oxygen ions are conducted through the oxygen ion conductingmembrane to the anode where they are recombined to form O₂, which iscollected and recovered.

While specific embodiments of the present invention have beenillustrated and described, numerous modifications come to mind withoutsignificantly departing from the spirit of the invention, and areincluded within its scope.

The invention claimed is:
 1. An electrochemical process for producingsynthesis gas comprising: decomposing water within an anode chambercomprising an electrochemically active anode according to the followingreaction: ½H₂O→¼O₂+H⁺+e⁻; removing oxygen from the anode chamber;transporting H⁺ ions from the anode chamber to an intermediate chambervia a cation exchange membrane; reacting Na₂CO₃ and H⁺ ions within theintermediate chamber according to the following reaction:H⁺+½Na₂CO₃→½CO₂+½H₂O+Na⁺; removing CO₂ from the intermediate chamber;transporting Na⁺ ions from the intermediate chamber to a cathodechamber; decomposing water within the cathode chamber comprising anelectrochemically active cathode according to the following reaction:Na⁺+H₂O+e⁻→NaOH+½H₂; removing H₂ from the cathode chamber; removing NaOHfrom the cathode chamber; and reacting CO₂ and H₂ to form synthesis gascomprising CO and H₂.
 2. The electrochemical process according to claim1, wherein the NaOH removed from the cathode is reacted with a source ofCO₂ to form Na₂CO₃.
 3. The electrochemical process according to claim 2,wherein the source of CO₂ is selected from atmospheric air, combustiongases, or aerobic decomposition gases.
 4. An electrochemical process forproducing synthesis gas comprising: decomposing water within an anodechamber according to the following reaction: ½H₂→¼O₂+H⁺+e⁻; removingoxygen from the anode chamber; reacting Na₂CO₃ and H⁺ ions within anodechamber according to the following reaction: H⁺+½Na₂CO₃→½CO₂+½H₂O+Na⁺ ata location a distance away from the anode but within the anode chamber,wherein the H+ ions react with Na₂CO the after passing through a cationexchange membrane; removing CO₂ from the anode chamber at a locationnear where it is produced; transporting Na⁺ ions from the anode chamberto a cathode chamber; decomposing water within the cathode chamberaccording to the following reaction: Na⁺+H₂O+e⁻→NaOH+½H₂; removing H₂from the cathode chamber; removing NaOH from the cathode chamber; andreacting CO₂ and H₂ to form synthesis gas comprising CO and H₂.
 5. Theelectrochemical process according to claim 4, wherein the NaOH removedfrom the cathode is reacted with a source of CO₂ to form Na₂CO₃.
 6. Theelectrochemical process according to claim 5, wherein the source of CO₂is selected from atmospheric air, hydrocarbon combustion gases, oraerobic decomposition gases.